Here’s one that’s pretty easy to update because we don’t know much more than when I posted the original review. That’s partly because it’s not exactly easy to get data on exposure and infection of marine mammals with SARS-CoV-2. I assume no one’s going to do an experimental study on such animals, and we also haven’t been able to get samples when there were potential issues related to captive animals (because some people have a desire not to know, since knowing means you might have to act, and that requires a plan…).
We therefore still know very little about this virus in marine mammals, but there are still some relevant issues to keep on the radar, even though it’s presumably not going to be a major animal health risk in this group, nor a significant human health risk in terms of animal-to-human transmission.
Are any marine mammals actually susceptible to SARS-CoV-2?
We don’t know. As I’ve discussed before, we can look at ACE2 receptors (the structures the virus uses to attach to cells to infect them) for clues regarding potential species susceptibility. We have to be cautious putting too much faith in predicted susceptibility from this method, and most ACE2 studies have not included marine mammals. However, a couple of studies ranked various marine mammals as having “high” potential susceptibility (Damas el al. 2020, Luan et al. 2020).
A more marine mammal focused modeling study ( predicted various whales, dolphins, seals and otters would be highly susceptible to SARS-CoV-2. Sea lions were lower risk, which might be a very good thing given how they congregate in large populations, often close to human populations. In contrast, they predicted other species, like beluga whales and bottlenose dolphins, may be even more susceptible to the virus than people. High risk species from this study also included a large number of species that are already vulnerable or endangered. et al. 2020, available in pre-print)
So, if marine mammals are potentially susceptible to SARS-CoV-2, will they actually be exposed?
That’s hard to say. However, this virus has spilled over into many animal species, including wildlife, so we need to think about this careful and consider if there are any ways to mitigate any risks of exposure. As with other species, the greatest risk of exposure of marine mammals is from infected people. There’s the potential for exposure from other infected wildlife if this virus establishes itself more in wild animal populations, but the biggest threat is still humans.
This is obviously of concern for a very select group of people, but human-to-marine mammal contact does occur with captive marine mammals and sometimes in field research. Any direct contact poses some risk of passing pathogens (e.g. viruses, bacteria) in either direction. We saw the potential for transmission through the human-to-marine mammal route a few years ago in an MRSA outbreak in dolphins and walruses that we investigated. If we can pass MRSA to marine mammals, we can presumably do the same with SARS-CoV-2. However, in the big picture, infection of captive marine mammals is of limited concern.
How could wild marine mammals get exposed to this virus?
Direct contact between wild marine mammals and people is pretty uncommon, but there are situations where people can have close, or even direct, contact with such animals, such as whale watching enterprises with animals that are habituated to being around people. The other potential concern is exposure to sewage. The SARS-CoV-2 virus doesn’t generally survive well outside of the body, but it will probably survive for a short period of time in sewage. We know that contact with human sewage can result in transmission of other pathogens from people to wild animals. The odds of infectious virus being present in sewage that makes it into the ocean at high enough levels to cause a problem are probably exceptionally low. But, we can’t say it’s zero (especially where there are sewage infrastructure challenges that lead to release of poorly treated or untreated sewage).
Overall, the risk of exposure of marine mammals to SARS-CoV-2 is likely very low, and it’s presumably mainly from the rare situations where people have direct contact with them.
What would the implications be if marine mammals were to be infected with SARS-CoV-2?
Infected marine mammals would likely only spread the virus over short distances and for short periods of time. A small whale pod poses much less risk than a large congregation of sea lions, where there are enough individuals for sustained transmission in the group.
However, since some marine mammal populations are highly threatened, an outbreak localized to an individual pod or small population of certain species could still have significant consequences if infection was associated with disease and their ability to survive. We have no idea about that either.
What about the risk to people from marine mammals?
The risk posed by marine mammals to people is likely negligible. We’re pooping in their habitat more than they’re contaminating ours in any way. Sure, an infected marine mammal would likely pose a risk to a person if there was direct contact, but the odds of that are very low. Outside of some very population-dense areas, I suspect the potential impact of marine mammal infections on human health would still be very low.
The potential for human-to-animal transmission of SARS-CoV-2 in these animals, no matter how small, can’t be ignored. Places with captive marine mammals should limit contact with them (just like they should be limiting human-to-human contact), and there obviously should be no contact with people who are infected or quarantined because they are high risk.
Similar precautions apply to field research involving marine mammals. This has been a tough situation for any wildlife field researcher, but our goal is to prevent problems, not react to them. We’re still better off limiting contact as much as possible at this stage. When contact with animals is required, we need to maximize protective measures (e.g. masks), minimize contact time, minimize the number of people involved, and do everything possible to make sure infected or otherwise high-risk people don’t participate.
Tourism is another area to address. “Whale watching” should be that: watching from a distance, not trying to get close enough to touch the animal. These animals don’t need any more threats from us – we’re doing a good enough job compromising their survival already without adding in a new infectious disease.
Image from: http://pachicosecotours.com/